NLog MemoryTarget maximum size

Question

Since I have a global exception handler that reports uncaught errors via e-mail, next step is to add some context to it by having some 10-20 last lines of log that are collected.

So I am using MemoryTarget like so:

MemoryTarget _logTarget;
_logTarget = new MemoryTarget();
_logTarget.Layout = "${longdate}|${level:uppercase=true}|${logger}|${message}${exception}";
LoggingRule loggingRule = new LoggingRule("*", LogLevel.Debug, _logTarget);
LogManager.Configuration.AddTarget("exceptionMemory", _logTarget);
LogManager.Configuration.LoggingRules.Add(loggingRule);
LogManager.Configuration.Reload();

Apps containing this should run forever, and if I leave logs in memory, unchecked, I'll have neatly designed memory leak.

How to address this? How to truncate MemoryTarget.Logs to have at most say 100 lines?

Answer 1

Your best bet is probably to write your own MemoryTarget... Something like this (untested) should work.

namespace NLog.Targets
{
    using System.Collections.Generic;

    [Target("LimitedMemory")]
    public sealed class LimitedMemoryTarget : TargetWithLayout
    {
        private Queue<string> logs = new Queue<string>();

        public LimitedMemoryTarget()
        {
            this.Logs = new List<string>();
        }

        public IEnumerable<string> Logs 
        { 
          get { return logs; }
          private set { logs = value; }
        }

        [DefaultValue(100)]
        public int Limit { get; set; }

        protected override void Write(LogEventInfo logEvent)
        {
            string msg = this.Layout.Render(logEvent);

            logs.Enqueue(msg);
            if (logs.Count > Limit)
            {
              logs.Dequeue();
            }    
        }
    }
}

This example is based on the NLog MemoryTarget, the source code for which you can find here:

https://github.com/NLog/NLog

NLog docs are here:

http://nlog-project.org/documentation/v2.0.1/

I didn't see anything like you are asking about in either location.